Regarding angle of attack, which statement is true?

• A. The angle of attack is fixed throughout a flight.
• B. The angle of attack is the angle between the wing's chord line and the aircraft's longitudinal axis.
• C. The angle of attack is measured relative to the horizon.
• D. The angle of attack is the angle between the chord line and the relative wind and changes during flight, affecting lift.

Answer: (D)

Angle of attack is defined as the angle between the wing’s chord line and the relative wind (the oncoming air). This angle isn’t fixed; as the aircraft changes pitch, airspeed, and flight conditions, the relative wind direction changes and so does the angle between the wing’s chord line and that wind. That angle directly affects lift: increasing the angle of attack increases lift up to a point, then if you push past the critical angle, the wing stalls and lift drops abruptly.

So the statement that correctly describes AoA is that it is the angle between the chord line and the relative wind and it changes during flight, influencing lift. It’s not measured relative to the horizon or to the aircraft’s longitudinal axis.